1. Field of the Invention
The invention relates to a control apparatus for an internal combustion engine, which includes an exhaust gas recirculation passage through which exhaust gas is recirculated back from an exhaust passage to an intake passage, and a method for controlling the same.
2. Description of the Related Art
There has been suggested an exhaust gas recirculation (EGR) system for an internal combustion engine, for example, a diesel engine. The exhaust gas recirculation system recirculates a portion of exhaust gas back from an exhaust passage to an intake passage to decrease the combustion temperature in the engine, thereby suppressing generation of NOx. For example, an EGR system that recirculates exhaust gas back to an intake system from an exhaust passage at a portion downstream of a catalyst (hereinafter, referred to as a “low-pressure loop EGR system”) has been suggested. Japanese Patent Application Publication No. 2005-146919 (JP-A-2005-146919) describes a technology related to a low-pressure loop EGR system. According to the technology, a control for supplying gas into a passage, through which a gas flow bypasses an intercooler, is executed during the transitional state, whereby the amount of exhaust gas contained in the gas taken into a combustion chamber is promptly adjusted to a desired amount. According to this technology, the bypass passage passes close by the engine.
However, the technology described in JP-A-2005-146919 has a disadvantage that the intercooler may corrode if the condensed water, which is obtained from the exhaust gas and recirculated by the low-pressure EGR system, is supplied to the intercooler. Such corrosion may occur if strongly acidic condensed water is supplied to the intercooler.